CN103595069B - Photovoltaic generating system grid side converter model predictive control method under unbalance voltage - Google Patents
Photovoltaic generating system grid side converter model predictive control method under unbalance voltage Download PDFInfo
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- CN103595069B CN103595069B CN201310575435.4A CN201310575435A CN103595069B CN 103595069 B CN103595069 B CN 103595069B CN 201310575435 A CN201310575435 A CN 201310575435A CN 103595069 B CN103595069 B CN 103595069B
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Abstract
The invention discloses photovoltaic generating system grid side converter model predictive control method under a kind of unbalance voltage.Drip irrigation device of the present invention is: according to sampling, line voltage and inhibit signal and initial power are given, and analytical Calculation obtains the reference current of converter AC; The predicted current under each voltage vector effect is obtained by forecast model, select the voltage vector making the absolute value of the difference of current reference value and current forecasting value minimum as optimal voltage vector by cost function, select switch position signal corresponding to optimal voltage vector as the switching signal controlling power device.Under unbalanced source voltage condition, ensure that DC bus-bar voltage is stable, current on line side is sinusoidal by controlling converter both sides power-balance, whole control procedure is based on two-phase rest frame, avoid rotating coordinate transformation, and control method does not comprise positive-negative sequence decomposition and phase-locked link, control structure is simple, and amount of calculation is less.
Description
Technical field
The present invention relates to photovoltaic generating system grid side converter model predictive control method under a kind of unbalance voltage, belong to electric and electronic power converting means control field.
Background technology
Compared with traditional vector control based on PI controller, Model Predictive Control has that structure is simple, rapid dynamic response speed, controller parameter without the need to advantages such as adjustments, be a kind of advanced control method with broad prospect of application.The operation that model predictive control method is applied to converter in photovoltaic generating system controls, and can obtain precisely Current adjustment effect fast.But all suppose that grid voltage three-phase balances when adopting model predictive control method to control, when unbalanced source voltage, DC bus-bar voltage produces two frequency multiplication pulsation, the output current of grid side converter distorts, and this will have a strong impact on the running status of photovoltaic generating system.Therefore, the control strategy that during unbalanced source voltage, grid side converter adopts should ensure that current on line side is sinusoidal, and direct voltage two frequency multiplication can be suppressed to pulse.Existing solution is the unbalance control method for vector control strategy, can not be applied in model predictive control method, and need rotating coordinate transformation process or positive-negative sequence decomposition operation is carried out to control variables, control system is comparatively complicated, and amount of calculation is larger.
Therefore, be necessary to design photovoltaic generating system grid side converter model predictive control method under a kind of unbalance voltage, under unbalanced source voltage condition, control method does not need positive-negative sequence decomposition operation and rotating coordinate transformation, DC bus-bar voltage can be suppressed to pulse, keep output current sinusoidal, ensure the Control platform of photovoltaic generating system.
Summary of the invention
The technical problem that the present invention solves there is provided photovoltaic generating system grid side converter model predictive control method under a kind of unbalance voltage, the method can suppress direct voltage two frequency multiplication to be pulsed, ensure current sinusoidal degree, effective minimizing current on line side harmonic wave, improves the Control platform of photovoltaic generating system grid side converter when unbalanced source voltage.
Technical scheme of the present invention is: photovoltaic generating system grid side converter model predictive control method under a kind of unbalance voltage, it is characterized in that comprising the following steps: (l), employing voltage sensor and current sensor detect three-phase power grid voltage, three phase network electric current and DC voltage respectively; (2) line voltage under abc/ α β conversion module obtains two-phase rest frame of the three-phase power grid voltage, step (l) detected and three phase network electric current and power network current; (3) line voltage under the two-phase rest frame, step (2) calculated obtains line voltage retardation through signal delay; (4), by the DC voltage that direct voltage reference value and step (1) obtain subtract each other, being multiplied with direct voltage reference value after PI controller by the voltage difference after subtracting each other obtains grid side converter active power reference value again; (5) the line voltage retardation that the line voltage, by step (2) obtained and step (3) obtain and the active power reference value that step (4) obtains, according to reference current calculating formula, obtain reference current; (6), using grid side converter model as forecast model, obtain the predicted current under each voltage vector effect by forecast model, select the voltage vector making the absolute value of the difference of current reference value and current forecasting value minimum as optimal voltage vector by cost function; (7) switch position signal corresponding to the optimal voltage vector, obtained by step (6) is as the switching signal controlling power device.
As further execution mode, the reference current calculating formula described in step (5) is as follows:
In formula,
,
.
Control method of the present invention is under unbalanced source voltage condition, ensure that DC bus-bar voltage is stable, current on line side is sinusoidal by controlling converter both sides power-balance, whole control procedure is based on two-phase rest frame, avoid rotating coordinate transformation, and control method does not comprise positive-negative sequence decomposition and phase-locked link, control structure is simple, and amount of calculation is less.
Accompanying drawing explanation
Fig. 1 is the structure chart of photovoltaic generating system, and Fig. 2 is the schematic diagram of control method of the present invention, and Fig. 3 is converter output current wave figure during employing control method of the present invention, and Fig. 4 is the DC bus-bar voltage oscillogram adopting control method of the present invention.
specific implementation method
Below in conjunction with accompanying drawing, the present invention will be further described.Photovoltaic power generation system structure as shown in Figure 1, photovoltaic array is connected with electrical network with step-up transformer through filter reactor by dc-dc converter, DC bus, grid side converter, and the output current of grid side converter directly determines the current harmonic content outputting to electrical network.
The Mathematical Modeling of grid side converter under the static alpha-beta coordinate system of two-phase is
(1)
In formula,
u g α,
u g βbe respectively the α of line voltage, beta-axis component;
u c α,
u c βbe respectively the α of converter output voltage, beta-axis component;
i g α,
i g βbe respectively the α of power network current, beta-axis component;
l g,
r gbe respectively reactor inductance value and line equivalent resistance.
Retardation under two-phase static alpha-beta coordinate system after line voltage, converter output voltage, power network current and each self-dalay 90 ° can be expressed as
，
(2)
，
(3)
，
(4)
In formula,
u g α,
u g βbe respectively the α of line voltage, beta-axis component amplitude;
u c α,
u c βbe respectively the α of converter output voltage, beta-axis component amplitude;
i g α,
i g βbe respectively the α of power network current, beta-axis component amplitude;
θ 1~
θ 6be respectively corresponding initial phase angle; Subscript " ' " represents the retardation of each variable;
ωfor line voltage angular frequency.
Converter active power of output
p cand reactive power
q cfor
(5)
Simultaneous formula (3) ~ formula (5)
(6)
In formula, Section 1 and Section 2 are respectively grid side converter active power of output DC component
and second harmonic component
.
Simultaneous formula (3), formula (4) and formula (6) can obtain
(7)
Wherein
(8)
In like manner, the DC component of grid side converter output reactive power can be obtained
with second harmonic component
for
(9)
Wherein
(10)
Photovoltaic generating system grid side converter control method schematic diagram when Fig. 2 is unbalanced source voltage.In figure,
u ga(
k),
u gb(
k),
u gc(
k) be respectively line voltage under three-phase static coordinate system;
u ca(
k),
u cb(
k),
u cc(
k) be respectively converter output voltage under three-phase static coordinate system;
i ga(
k),
i gb(
k),
i gc(
k) be respectively power network current under three-phase static coordinate system;
u dc(
k) be DC bus-bar voltage;
p *(
k) be active power reference value;
cfor DC bus capacitor.Outer voltage adopts PI controller to direct voltage
u dc(
k) regulate, and provide reference power for current regulator
p *(
k).Current regulator is by grid side converter model, electric current under the different voltage vector effect of subsequent time is predicted, adopt the result of cost function to prediction to evaluate and optimize, and select optimum on off state as the control signal of subsequent time power switch.
If the control system sampling period is
t s, current sampling instant is
k, then
t=
kT s.The discrete mathematical model that can be obtained grid side converter by formula (1) is
(11)
Can predict according to formula (11) and adopt different voltage vector
u c α
i (
k),
u c β
i (
k) time, the current value of system subsequent time
i m α
i (
k+ 1),
i m β
i (
k+ 1), subscript
i=1,2 ..., 7.
Definition cost function is shown below
(12)
In formula, subscript "
*" represent reference value,
,
be
kthe reference current in+1 moment, because this value is
kmoment is unknown, generally adopts
kthe reference current in moment
,
replace.
Model Predictive Control Algorithm is in each switch periods circulation primary, its operation principle is: according to the walk-off-mode pattern (11) of control object, electric current under the different on off state of PREDICTIVE CONTROL object subsequent time, adopt cost function to assess predicting the outcome under different on off state, and select the voltage vector making cost function minimum as the output of controller.
Model Predictive Control of the present invention is according to grid side converter power output equilibrium principle computing reference electric current.Pulse to suppress direct voltage two frequency multiplication, reduce power network current distortion, need consider during computing reference electric current that converter active power of output DC component is constant, harmonic component is zero, control reactive power DC component is zero to ensure grid side converter unity power factor simultaneously, namely
(13)
From formula (7), for making
can make
.
Can be obtained with formula (13) by formula (7), formula (9)
(14)
Solve above formula and obtain reference current
,
with reference current retardation
,
be respectively
(15)
(16)
Wherein,
.
Because converter output voltage exists a large amount of switch harmonic, there is comparatively big error in the reference current calculated by formula (15).In order to avoid carrying out Delay computing to converter output voltage, reduce the reference current error of calculation, the retardation of converter output voltage is calculated by line voltage retardation and power network current, due to the equivalent resistance on filter reactor
r gresistance is very little, can ignore.According to formula (1) ~ formula (4), and replace power network current with reference current, converter output voltage and retardation thereof can be expressed as
，
(17)
Obtained by formula (14) ~ formula (17)
，
(18)
In formula,
,
.
Formula (18) is substituted into formula (15), can obtain
(19)
In formula,
.
From formula (19), the inductance value according to line voltage, line voltage retardation and filter reactor can in the hope of reference current.During unbalanced source voltage, the active power that the model predictive controller of design considers net side and filter reactor total based on formula (19) pulse, ensures that converter active power of output balances, thus suppression DC voltage ripple.
Carrying out discretization analysis to formula (19), can to obtain reference current calculating formula as follows
(20)
In formula,
,
.
The reference current of formula (20) substituted into formula (12) and adopts cost function to assess predicting the outcome under different on off state, selecting the voltage vector making cost function minimum as optimal voltage vector.Using switch position signal corresponding for optimal voltage vector as the switching signal controlling power device
According to above analysis, the control method of photovoltaic generating system grid side converter specifically comprises the steps:
L (), employing voltage sensor and current sensor detect three-phase power grid voltage respectively
u ga(
k),
u gb(
k),
u gc(
k), three phase network electric current
i ga(
k),
i gb(
k),
i gc(
k) and DC voltage
u dc(
k);
(2) three-phase power grid voltage, step (l) detected
u ga(
k),
u gb(
k),
u gc(
k) and three phase network electric current
i ga(
k),
i gb(
k),
i gc(
k) line voltage under abc/ α β conversion module obtains two-phase rest frame
u g α(
k),
u g β(
k) and power network current
i g α(
k),
i g β(
k);
(3) line voltage under the two-phase rest frame, step (2) calculated
u g α(
k),
u g β(
k) obtain line voltage retardation through signal delay
u ' g α(
k),
u ' g β(
k);
(4), by direct voltage reference value
u * dc(
k) DC voltage that obtains with step (1)
u dc(
k) result of subtracting each other, after PI controller again with direct voltage reference value
u * dc(
k) being multiplied obtains grid side converter active power reference value
p * (
k);
(5) line voltage, obtained by step (2)
u g α(
k),
u g β(
k) and the line voltage retardation that obtains of step (3)
u ' g α(
k),
u ' g β(
k) and the active power reference value that obtains of step (4)
p * (
k), according to reference current calculating formula, obtain reference current
i * g α(
k),
i * g β(
k).
(6), the predicted current under each voltage vector effect is obtained by grid side converter forecast model
i m α
i (
k+ 1),
i m β
i (
k+ 1), wherein subscript
i=1,2 ..., 7.Pass through cost function
g i (
k) select to make current reference value
i g α * (
k+ 1),
i g β * (
k+ 1) with current forecasting value
i m α
i (
k+ 1),
i m β
i (
k+ 1) voltage vector that the absolute value of difference is minimum
u c α(
k),
u c β(
k) as optimal voltage vector;
(7), with the optimal voltage vector that step (6) obtains
u c α(
k),
u c β(
k) corresponding switch position signal is as the switching signal controlling power device.
As further execution mode, the reference current calculating formula described in step (5) is as follows:
In formula,
,
.
Fig. 3 is the power network current oscillogram adopting control strategy of the present invention, as seen from Figure 3, adopts control algolithm of the present invention, and the sine degree of electrical network three-phase current is better, and harmonic content is suppressed preferably.
Fig. 4 is the DC voltage oscillogram adopting control strategy of the present invention, as can be seen from Figure, when unbalanced source voltage, the pulsation of DC bus-bar voltage two frequency multiplication is less, control method of the present invention in unbalanced source voltage situation, can obtain stable DC bus-bar voltage.
In sum, control method of the present invention can effectively suppress DC bus-bar voltage to be pulsed under unbalanced electric grid voltage, and reduce three-phase current distortion, enhance the serviceability of photovoltaic generating system grid side converter, and structure is simple, amount of calculation is little.
Claims (1)
1. photovoltaic generating system grid side converter model predictive control method under unbalance voltage, it is characterized in that comprising the following steps: (l), employing voltage sensor and current sensor detect three-phase power grid voltage, three phase network electric current and DC voltage respectively; (2) line voltage under abc/ α β conversion module obtains two-phase rest frame of the three-phase power grid voltage, step (l) detected and three phase network electric current and power network current; (3) line voltage under the two-phase rest frame, step (2) calculated obtains line voltage retardation through signal delay; (4) result of, by the DC voltage that direct voltage reference value and step (1) obtain subtracting each other, is multiplied with direct voltage reference value again and obtains grid side converter active power reference value after PI controller; (5) the line voltage retardation that the line voltage, obtained by step (2) and step (3) obtain and the active power reference value that step (4) obtains, according to reference current calculating formula, obtain reference current, reference current calculating formula is:
In formula,
,
; (6), using grid side converter model as forecast model, the predicted current under each voltage vector effect is obtained by forecast model, select the voltage vector making the absolute value of the difference of current reference value and current forecasting value minimum as optimal voltage vector by cost function, wherein cost function is
In formula,
,
be
kthe current reference value in+1 moment,
i m α
i (
k+ 1),
i m β
i (
k+ 1) be
kthe current forecasting value in+1 moment; (7) switch position signal corresponding to the optimal voltage vector, obtained by step (6) is as the switching signal controlling power device.
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| AT513776B1 (en) * | 2014-04-08 | 2015-09-15 | Avl List Gmbh | Method and controller for model-predictive control of a multiphase DC / DC converter |
| CN103956919A (en) * | 2014-04-15 | 2014-07-30 | 中国矿业大学 | Simplified model forecasting control method of network voltage unbalance three-level rectifier |
| CN104181374B (en) * | 2014-08-08 | 2017-02-15 | 合肥工业大学 | Method for detecting and separating positive and negative sequence components of grid voltage of three-phase neutral-line-free system |
| CN106549400B (en) * | 2016-12-10 | 2018-11-02 | 三峡大学 | A kind of control method of the distribution static synchronous compensator based on voltage prediction |
| CN107204711B (en) * | 2017-07-04 | 2019-09-17 | 北京千驷驭电气有限公司 | Current prediction method and device based on extension z-transform |
| CN109004852B (en) * | 2018-06-25 | 2020-04-21 | 国网浙江省电力有限公司电力科学研究院 | Model prediction control strategy of modular multilevel converter |
| CN109802584B (en) * | 2019-03-26 | 2020-09-29 | 大连理工大学 | Three-phase VSR unified MPC method capable of realizing AC-DC side performance consideration |
| CN110048466B (en) * | 2019-05-30 | 2021-09-24 | 湖南大学 | Prediction control method for grid-side converter model of double-fed wind power generation system |
| CN110429836B (en) * | 2019-07-23 | 2020-04-28 | 合肥为民电源有限公司 | Control method and device of three-phase PWM rectifier |
| CN111525591B (en) * | 2020-04-30 | 2023-03-14 | 陕西科技大学 | VSC control method under three-phase unbalanced state |
| CN111969594B (en) * | 2020-05-20 | 2022-03-15 | 国网山东省电力公司青岛供电公司 | Control method and system of back-to-back converter |
| CN112165271B (en) * | 2020-10-09 | 2021-08-20 | 河南科技大学 | Grid-connected converter system and model prediction control method thereof |
| CN114844115B (en) * | 2022-07-01 | 2022-11-15 | 浙江大学 | Photovoltaic converter network construction control method and device based on model predictive control |
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